The goal of this project is to develop new or improved methods for the determination of moisture in biological products. A low residual moisture is necessary for the stability, viability and potency of the freeze-dried biological product. For samples with uncomplicated thermogravimetric analysis (TG) curves, TG results have been shown to correlate with coulometric Karl Fischer results. Karl Fischer and TG moisture results may be different from the gravimetric moisture result for the same freeze-dried product due to the fact that different types of moisture (physically adsorbed or chemically bound moisture)are being measured. A new capillary TG/MS interface applicable to this analysis has been developed in our laboratory. This interface allows continuous monitoring of the ion intensities of mass peaks m/e=18 (water) and m/e=44 (carbon dioxide) for the determination of residual moisture in freeze-dried biological products. Measurement of vapor pressure moisture in space above freeze-dried cake is being researched.